As defiant Egyptian protesters laid siege to government buildings and took to the streets to protest against the government, President Hosni Mubarak announced he has asked his government to resign.

The embattled president, who has run Egypt for the last 30 years, spoke for the first time since mass demonstrations broke out on Tuesday. Although many of the demonstrators demanded he step down, the 82-year-old Mubarak gave no indication that he will relinquish his post.

President Obama said tonight that he spoke to Mubarak after the Egyptian president spoke to his country and vowed to lay the groundwork for reforms to tackle the economy, unemployment and poverty in the country.

Obama said he told Mubarak "you have a responsibility to bring meaning to those words" and to make his promises come true.

He also called on the Egyptian to end its blockage of cell phones and the Internet, lecturing Mubarak that his people "have rights that are universal, rights to peaceful assembly... free speech and the right to determine their own destiny."

"There must be reform," Obama said bluntly, and at another point warned that the "U.S. will stand up for rights of Egyptian people."

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Mubarak's appearance on Egyptian television was a remarkable turnaround from Tuesday when the protests began and appeared to pose little threat to the regime.

"These demonstrations shouldn't have happened, because of the big gaps in freedom that were given," Mubarak said, according to a rough translation of his address to the nation. "As the president of this country and with all the power that the Constitution has given me, I assure you that I'm working for the people and giving freedoms of opinions, as long as we are respecting the law."

Mubarak appealed for calm, saying there's a "fine line between freedom and chaos."

"I am on the side of freedom of the people, but also of the security of Egypt. And I will not let anything happen that threatens the security of the country," he said.

Mubarak took to the camera after a tough crackdown by government forces that prompted the Obama administration to reconsider the $1.5 billion in aid it gives to Egypt.

But his speech is unlikely to appease the massive crowds, angry and frustrated at the country's dire economic situation, high food prices, rising unemployment and decades of corruption and poverty.

The U.S. made clear its disapproval of its ally's use of force to break up the massive protests, but administration officials refused to directly implicate President Hosni Mubarak, whose ouster is the focal point of this week's protests.

"Violence is not the response," White House Press Secretary Robert Gibbs said today. "A space has to be created to address those...very legitimate grievances."

The Egyptian government imposed a nationwide curfew tonight after a day of fierce clashes but protesters defied it and continued to pour out into the streets.

In Cairo, thousands of protesters, frustrated with high unemployment, hunger and corruption, poured out of mosques after Friday prayers chanting "out, out, out." They were met with by armored vehicles and police firing a barrage of rubber bullets, tear gas and water cannons. But the crowds, seething with anger, were unrelenting and retaliated by throwing rocks at the police.

Tanks Surround U.S. Embassy at Request of U.S. Diplomats

The violence got worse as the day wore on. Restaurants on the Nile River set on fire, and when it seemed the clashes were peaking silence fell as protestors stopped to pray.

Despite the curfew and the fact the army was called in for the first time ever to quell the crowds, protesters set tires ablaze in the street and the ruling party's National Democratic Party headquarters was engulfed in flames.

"Thirty years is enough. We hate these people. We hate all this government," said one protester. "We want a complete change for all of them."

Unlike the police, that has clashed with protesters all week, the army is loved and was cheered on by demonstrators. Some even attempted to engage security forces and soldiers to sway them into joining the protests, according to news reports.

In the city's capital, protesters appeared to be gathering in the city center seemingly without any resistance from security forces though news reports showed multiple Armored Personnel Carriers entering downtown Cairo.

Protesters gathered around the Egyptian Museum to protect the artifacts housed inside the building amid fear of looting.

"We are Egyptians and this is the Egyptian Museum and we are standing here and calling for the army to come as soon as possible," said one protester. "We will not leave until the Egyptian army arrive."

Al Jazeera reported that more than 850 people have been wounded. The death toll is believed to be very small but is unknown.

A number of Egyptians expressed frustration with the U.S. government and President Obama, telling ABC News that for all the talk about freedom, the U.S. is not supporting it in Egypt. One protester pointed to the fact that the tear gas canisters being used by the police are made in the U.S.

Two U.S. officials tell ABC News that the Egyptian tanks surrounding the U.S. embassy are there at the behest of the United States to protect the compound.

The Egyptian government has shut down Internet and cell phone service in the country, leaving landlines and satellite as the only form of communication.

Earlier today, Secretary of State Hillary Clinton called on the Egyptian government to open cell phone and internet lines, and also urged protesters to march peacefully, saying "violence will not make these grievances go away." But she dodged a question on whether Mubarak's 30-year rule is coming to an end as both the State Department and White House cancelled their afternoon briefings.

"We are deeply concerned about the use of violence by the Egyptian police and security forces against protesters, and we call on the Egyptian government to do everything in its power to restrain the security forces. At the same time, protestors should also refrain from violence and express themselves peacefully," Clinton said, in the most forceful tone she has employed since protests began this week.

"As we have repeatedly said, we support the universal human rights of the Egyptian people, including the right to freedom of expression, of association, and of assembly," she added. "We urge the Egyptian authorities to allow peaceful protests and to reverse the unprecedented steps it has taken to cut off communication."

But Clinton dodged ABC News' question about the United States condemning the crackdown and wouldn't respond to questions on Mubarak's fate.

Egypt Clashes Escalate

Instead, she provided a lengthy reiteration of her opening statement about the need for the government to engage with its people, for both sides to show restraint, and how the U. S. wants to be a partner in the reform.

Gibbs said Obama had not spoken to Mubarak but administration officials had been in touch with various entities of the Egyptian government.

The United States wants Mubarak, a staunch U.S. ally, to make reforms now to appease the protestors before they push him out of power. The administration has tried to support the right of the demonstrators to gather and protests, but does not want to see Mubarak, an important ally in the region, fall and so they have urged him in public and in private to reform before it is too late.

The best case scenario for the administration is he makes the reforms and stays in power, but if he is toppled, analysts question whether the new leaders that fill the power vacuum will be as strongly allied with the U.S.

The United States issued a travel warning to Egypt and urged Americans to defer non-essential travel to the country because of the ongoing protests.

Today's gathering was the largest since the demonstrations started on Tuesday, and the largest the country has seen in decades. Images showed pictures of protesters kneeling to pray as riot police looked on. Protesters were seen rocking an armored vehicle as another armored vehicle tried to scatter the demonstrators by driving through them, knocking several down.

In a drastic move to suppress the protests, Mubarak enforced a night curfew, from 6 p.m. to 7 a.m. in Cairo, Alexandria and Suez, where some of the most violent clashes occurred, and then extended it to all of the country. Egypt state TV announced that Mubarak has ordered the army onto the streets to help police enforce curfew, the first time ever the government has made such a move.

But the crackdown has made the protesters even more determined. Defying the curfew, protesters continue to gather and march hours after it went into effect and government forces fired on them with tear gas.

At least two buildings on the Nile River in Cairo went up in flames, as did the head office of Mubarak's National Democratic Party. The Egyptian army placed armored trucks in front of the state television building and the Ministry of Interior, as demonstrators attempted to enter those buildings, the Parliament and the National Democratic Party's head office.

Mubarak, Egypt's commander-in-chief, has not been seen since the protests began Tuesday. Reports said he was to address the nation today but that has yet to be confirmed. Mubarak has stayed mostly silent amid concern that his speaking would further incite the protesters and end any hopes of a compromise, as was the case in Tunisia recently when Ben Ali's strategy to communicate with the nation backfired, and he ousted from power.

Egypt Protests Mirror Those in Tunisia

Protests have spread through Arab countries in recent weeks, starting with street demonstrations in Tunisia which forced its long-time president to flee. Since then, protests have erupted in Egypt and Yemen, all U.S. allies.

But unlike in Tunisia, the police and the military are on the side of Mubarak's government, an administration that is very strong and is not expected to yield power easily.

While the United States was quick to support the aspirations of Tunisian protesters once the government there was toppled, Egypt is a different story.

As one of only two Arab countries who recognize Israel, it plays a critical role in the Mideast peace process and is one of the United States' strongest allies, and one of the lead recipients of its foreign aid, in the region.

On Thursday, Obama reiterated the two countries close relationship, and that the he's "always said" to Mubarak that reform, both politically and economically, is essential for Egypt.

"Egypt's been an ally of ours on a lot of critical issues," Obama said. "President Mubarak has been very helpful on a range of tough issues in the Middle East. But I've always said to him that making sure that they are moving forward on reform -- political reform, economic reform -- is absolutely critical to the long-term well being of Egypt."

Mubarak was invited to the White House to help launch the latest round of Israeli-Palestinian talks last year. Egypt is also considered a regional leader, albeit fading, and a key voice in a strategically important area. Recent documents released by Wikileaks show that the United States has held a nuanced view of Mubarak's Egypt, tolerating human rights abuses and the veneer of democracy in exchange for geopolitical influence.

The U.S. government has also previously clashed with Nobel Peace Prize winner Mohammed ElBaradei, one of the country's leading voices on democracy who was reportedly placed under house arrest today.

ElBaradei returned home to Egypt Thursday after a month-long absence to join the protests.

"We are not waiting for help or assistance from the outside world," he said, in a direct swipe at the United States, accused by many here of supporting its closest Arab ally and not the people yearning for freedom. "But what I expect from the outside world is to practice what they preach, is to defend the right of the Egyptians, for their universal values: Freedom, dignity, social justice and the rule of law."

While he and the International Atomic Energy Agency jointly won the Nobel Peace Prize in 2005 for their efforts to prevent the militarization of nuclear energy programs, the Bush administration and later the Obama administration frequently clashed with ElBaradei because they believed he was watering down the UN watchdog's reports on Iran's nuclear program.

To his supporters, ElBaradei and his return to Egypt represents the best chance to galvanize a weak and diverse opposition. To his critics, he is an opportunist who has spent too much time in Vienna.

In Washington, D.C., Egyptian-American groups called on the Obama administration to condemn the Mubarak regime and stand on the side of protestors.

"There's a blood that's been shed in Egyptian streets and that blood is in our hands," said Dr. Samia Harris, vice president of the Alliance of Egyptian Americans. "Please stand by the right side of history. Stand by the Egyptian people."